Seismic assessment of hollow core concrete bridge piers

Hollow core concrete bridge piers are traditionally believed to be vulnerable to seismic action. However, the seismic vulnerability of such piers has not been investigated fully. In this paper, an analytical model to assess seismic vulnerability of hollow core concrete bridge pier is developed. The model is validated with available experimental results. Code recommendations for hollow core bridge piers are evaluated. It is shown that confinement reinforcement requirements in the codes are sometimes highly conservative and sometimes non-conservative. However, the recently developed confinement reinforcement equations for solid bridge piers at Sherbrooke University can be applied for economic and safe design. It is demonstrated that hollow core bridge piers are not as vulnerable as it is traditionally believed. Such piers can attain expected ductility, if designed properly

Estimation of near-surface attenuation in bedrock for analysis of intraplate seismic hazard

The significance of near-surface attenuation in bedrock, as distinct from attenuation in unconsolidated soft soil sediments, has been identified. The k parameter, which characterizes the extent of this attenuation mechanism, is generally difficult to measure, particularly in regions of low and moderate seismicity. Empirical correlation of k with the near-surface shear wave velocity parameter in rock has been developed using global information obtained from limited independent studies. The influence of shaking intensity on the value of k has been found to be negligible in conditions that are consistent with the average seismicity of Australia (as also for other intraplate regions). Thus, adjustment in the value of k to account for variations in earthquake magnitude, or the intensity of ground shaking, has not been recommended for intraplate conditions. In parallel with the empirical correlations, values of k have also been obtained from calibration analyses employing stochastic simulations of the seismological model, along with onedimensional non-linear shear wave analyses of the rock layers. Good agreement in the values of k obtained from the different approaches has been demonstrated. The correlation of k with the near-surface shear wave velocity of rock, as recommended in this paper, has thereby been reaffirmed

Investigation of engineering properties of normal and high strength fly ash based geopolymer and alkali-activated slag concrete compared to ordinary Portland cement concrete

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength

Seismic vulnerability of hollow core concrete bridge piers

Hollow core concrete bridge piers are traditionally believed to be vulnerable to seismic action. However, seismic vulnerability of such piers has not been investigated fully. In this paper, a modeling method to assess seismic vulnerability of hollow core concrete bridge pier is developed. The method is validated with available experimental results. Code recommendations for hollow core bridge piers are evaluated. It is shown that confinement reinforcement requirements in the codes are sometimes highly conservative and sometimes non-conservative. However, the recently developed confinement reinforcement equations for solid bridge pier at Sherbrooke University can be applied for economic and safe design. It is demonstrated that hollow core bridge piers are not as vulnerable as it is believed traditionally. Such piers can attain expected ductility, if designed properly

Optimal performance for cost effective seismic design of bridges

A systematic approach is proposed for evaluating the cost-effectiveness of existing design codes from the perspective of lifecycle cost consideration. In the life cycle cost formulation, cost of construction, damage cost, road user cost, as well as discount cost over the design life of the bridge are considered. The optimal performance is selected on the basis of minimum life cycle cost. The performance of a typical two-span bridge designed according to a current code provision for different earthquake ground motion levels is predicted and optimal target performance is selected based on life cycle cost with different assumptions of user cost. It is demonstrated that life cycle cost should be considered in the design phase of a new structure or of a structure to be retrofitted, and the target performance significantly depends on the expected average daily traffic for the road

Confinement reinforcement for bridges in medium to high seismicity zone based on new CSA A23.3-04 approach

Recent advances in confinement reinforcement of building columns have resulted in changes in Canadian code for Design of Concrete Structures CSA A23.3-04. Bridge columns and piers may also take advantage of these advances. The purpose of this paper is to use a comparable approach to propose new equations to be introduced in future Canadian bridge design code. The adopted approach for transverse reinforcement is based on the recently developed uniaxial confinement model for concrete column at Sherbrooke University. Parametric studies have been carried out on some typical bridge columns and piers to develop equations for confinement reinforcement. An intermediate level of ductility (moderate ductility) for bridge columns and piers has been introduced, similar to that in CSA A23.3-04 building design code. Confinement reinforcement for this level of ductility has been found to be less stringent than that for ductile level. This level of ductility is suitable for regions of low to medium seismicity. The adopted approach is supported by experimental results and will provide the designer more flexibility but economical and safer seismic design of bridge columns and piers